1. Field of the Invention
This invention relates to the reproduction and storage of video signals. More particularly, this invention relates to the reproduction and storage of coded video signals, such as those that have undergone sub-band coding or discrete cosine transformation.
2. Description of the Prior Art
A task which users of video reproduction and storage systems often want to perform is to locate a particular point within the recorded video signal. To assist in this task it is known to provide some types of system with the ability to display a picture from the current position of the recording medium during shuttle mode operation. When searching through a recorded video signal, such a facility allows the sequence of action to be followed and the point being searched for to be more easily identified.
An example of such shuttle mode playback can be found in some domestic analog video tape recorders. In these systems the video signal is recorded in slanting tracks with position along the tracks corresponding to position within the field. Due to the high speed movement of the tape in shuttle mode, the path of the rotating read head doesn't follow complete tracks to allow the information for one field of the image to be recovered, but instead follows a course intersecting several tracks. However, since the position of the analog signals along each track corresponds to the position in the field, then the signal read from the different tracks intersected represents portions of the complete image from successive fields. Accordingly, if this signal read is output to a display device then it forms a recognisable image. The image produced is interspersed with noise bars corresponding to crossings between tracks, but nevertheless allows the point in the tape being searched fop to be readily identified.
Providing a picture during shuttle operation in a system operating with a frequency separated, and possibly compressed, video signal cannot be achieved in the same manner as in the domestic analog video recorder. Again, the read head is unable to follow complete tracks, but in this case there is no simple relationship between position along the tracks and position in the picture, since the image has been split into different frequency components, as well as possibly being quantised and encoded for compression purposes.